1. Field of the Invention
The present invention relates to a method and plant for recycling waste parts, with a coating made of synthetic resin, especially with a method and plant enabling continuous recycling.
2. Description of the Prior Art
Recently, it has become necessary to reuse waste parts made of synthetic resin, for environmental reasons, and it is general to separate waste parts and reuse them as material for new products. It is, furthermore, general to coat products with thermosetting coating to add to the beauty of the products.
In the case of liquefying waste parts with a coating, a thermosetting coating is not decomposed. Therefore, material strength is degraded when synthetic resins containing undecomposed coatings are reused.
For instance, in a cold district, the material strength of bumpers made of synthetic resins containing undecomposed coatings is lower than that of bumpers made of synthetic resin without the coatings.
The degradation of material strength can be avoided if coating is removed, but perfect removal of the coating is too difficult.
Although coatings can be mechanically removed by shot blasting etc., it not only takes a long time but is impossible to perfectly remove the coating when parts have complicated shapes. Mechanical removal, therefore, is unsuitable for mass recycling.
Although removal of the coating with organic acid has been proposed, it causes environmental pollution.
To solve the above-mentioned problem, the present applicant has already proposed a method for recycling synthetic resin parts, that is, the coating thereof is hydrolyzed and kneaded into synthetic resin chips (See Japanese Patent Application No. 3-192431).
To shorten the process time, hydrolysis must be performed under a relatively high temperature atmosphere, but this is unavoidable if the synthetic resin is to liquefy.
When hydrolyzed synthetic resin is taken out from the vessel for hydrolyzing after cooling-down, it is impossible to reuse the synthetic resin as raw material without crushing, because it is again solidified.
On the other hand, when liquefied synthetic resin is reused as a raw material, it is necessary to keep a flow path of the liquefied synthetic resin at a relatively high temperature, but this requires more energy consumption.